The present invention relates essentially to a method of controlling the methanic fermentation of various organic materials.
It is also directed to an equipment for carrying out this method.
There has already been proposed to operate fermentors by using mathematical models taking into account the diversity of the materials to be treated as well as the fluctuations of the catalytic behaviors of the micrc-organisms.
It is also known for operating the fermentors to provide an anaerobic fermentation model for diluted substrates or substrates of simple nature but not for concentrated or complex organic materials.
These models may integrate one or several populations of micro-organisms. They may or may not take into account the physical-chemical equilibriums, the inhibiting effect of the pH or of the volatile fatty acids such as the acetic acid which are essential metabolic intermediaries.
There are further known purely biological mathematic models for diluted substrates in one operating step, based upon the acetate concentration or in two operating steps, namely acidogenesis and methanogenesis from simple substrates such as glucose. These models take into account an inhibition of the methanogeneous activity by the non-ionized volatile fatty acids but they do not integrate the pH as a state variable in relation to the physical-chemical balances.
There are further known biological mathematical models for diluted substrates of the methanization taking into account the physical-chemical balances thus permitting to integrate the pH as a state variable and to contemplate its inhibiting part.
These latter models, however, do not take into account the inhibiting effect of the non-ionized volatile fatty acids such as the acetic acid.
But none of the models referred to hereinabove integrates the combination of physical-chemical balances, of the pH as a state variable and of the inhibiting effect of the non-ionized volatile fatty acids and/or takes into account the case of the concentrated or complex organic materials.
It is further known that the operation of industrial methanization fermentors necessarily requires a great number of complementary physical-chemical measurements and analyses and in particular the measurement of:
the amount of the biogas produced and its quality (percentage of methane and percentage of carbon dioxide), PA1 the pH and the temperature, PA1 the quality of the processed inputs and outputs, and PA1 the volatile fatty acids content (AGV) of the fermentation medium and/or the hydrogen percentage of the produced biogas. PA1 the maximum methanogenous specific growth rate, PA1 the constant of inhibition of the methanogeneous bacteria, PA1 the saturation constant of the methanogeneous bacteria, and PA1 the yields or efficiency outputs expressed as the CH.sub.4 /biomass ratio, as the CO.sub.2 /biomass ratio and as the substrate/biomass ratio.
In a general manner the operation of the fermentors based upon earlier known models is not satisfactory in that the models are not adjusted to the specific operating conditions of the installation site of the fermentors.